Commercially available cleaning equipment in the heat treatment industry is generally water-based cleaning machines, and only a few are hydrocarbon-solvent cleaning machines.
With respect to water-based cleaning machines, water is used as a cleaning medium. Oil cannot dissolve in water, but water-based cleaning machines are mostly used to clean workpieces after oil quenching. Therefore, to improve a cleaning effect, it is necessary to adjust the temperature of water and add a cleaning agent (or a rust inhibitor) to the water.
A major defect of a water-based cleaning machine is water pollution. The reason is that after the cleaning machine works a long time, water contains emulsified oil, and therefore a cleaning effect is severely affected. Therefore, water needs to be replaced regularly. Waste oil (quenching oil) after cleaning needs to be treated by qualified treatment units and cannot be recycled and reused. As a result, use costs are greatly increased. In addition, the cleanliness of a workpiece cleaned by using a water-based cleaning machine may fail to satisfy a requirement, as blind holes or tiny gaps of some workpieces basically cannot be cleaned. Consequently, water-based cleaning machines are not applicable to those industries having high cleanliness requirements.
With respect to hydrocarbon-solvent cleaning machines, a hydrocarbon solvent is used as a cleaning medium. The hydrocarbon solvent is a petroleum hydrocarbon mixture and can dissolve quenching oil, so that a cleaning effect is very desirable and a cleaned workpiece has a very clean surface. As the hydrocarbon solvent has a low flash point, a heating manner is used to remove the hydrocarbon solvent through distillation, and the quenching oil that remains can still be recycled and reused.
A hydrocarbon-solvent cleaning machine has a desirable cleaning effect and does not produce pollution. However, the hydrocarbon solvent is a flammable and explosive substance. Therefore, a user needs to have protection to during use and a better option is required.
Chinese Patent Application No. 200810226688X discloses a supercritical-carbon-dioxide purging and cleaning machine for semiconductors, comprising a cleaning chamber and a separation chamber. The cleaning chamber and the separation chamber are connected through a sealed carbon dioxide outlet pipe. A nozzle is provided on the cleaning chamber. Carbon dioxide is directly sprayed through the nozzle to a silicon wafer to be cleaned at the bottom of the cleaning chamber. However, air may enter the cleaning chamber during cleaning, which adversely affects a cleaning effect.